scholarly journals Climate change will cause non-analog vegetation states in Africa and commit vegetation to long-term change

2020 ◽  
Vol 17 (22) ◽  
pp. 5829-5847
Author(s):  
Mirjam Pfeiffer ◽  
Dushyant Kumar ◽  
Carola Martens ◽  
Simon Scheiter
Keyword(s):  
Vegetation Change ◽  
Structural Changes ◽  
Equilibrium States ◽  
Tree Cover ◽  
Environmental Drivers ◽  
Vegetation Model ◽  
Dynamic Global Vegetation Model ◽  
Lag Times ◽  
Over Time

Abstract. Vegetation responses to changes in environmental drivers can be subject to temporal lags. This implies that vegetation is committed to future changes once environmental drivers stabilize; e.g., changes in physiological processes, structural changes, and changes in vegetation composition and disturbance regimes may happen with substantial delay after a change in forcing has occurred. Understanding the trajectories of such committed changes is important as they affect future carbon storage, vegetation structure, and community composition and therefore need consideration in conservation management. In this study, we investigate whether transient vegetation states can be represented by a time-shifted trajectory of equilibrium vegetation states or whether they are vegetation states without analog in conceivable equilibrium states. We use a dynamic vegetation model, the aDGVM (adaptive Dynamic Global Vegetation Model), to assess deviations between simulated transient and equilibrium vegetation states in Africa between 1970 and 2099 for the RCP4.5 and 8.5 scenarios using regionally downscaled climatology based on the MPI-ESM output for CMIP5. We determined lag times and dissimilarity between simulated equilibrium and transient vegetation states based on the combined difference of nine selected state variables using Euclidean distance as a measure for that difference. We found that transient vegetation states over time increasingly deviated from equilibrium states in both RCP scenarios but that the deviation was more pronounced in RCP8.5 during the second half of the 21st century. Trajectories of transient vegetation change did not follow a “virtual trajectory” of equilibrium states but represented non-analog composite states resulting from multiple lags with respect to vegetation processes and composition. Lag times between transient and most similar equilibrium vegetation states increased over time and were most pronounced in savanna and woodland areas, where disequilibrium in savanna tree cover frequently acted as the main driver of dissimilarities. Fire additionally enhanced lag times and dissimilarity between transient and equilibrium vegetation states due to its restraining effect on vegetation succession. Long lag times can be indicative of high rates of change in environmental drivers, of meta-stability and non-analog vegetation states, and of augmented risk for future tipping points. For long-term planning, conservation managers should therefore strongly focus on areas where such long lag times and high residual dissimilarity between most similar transient and equilibrium vegetation states have been simulated. Particularly in such areas, conservation efforts need to consider that observed vegetation may continue to change substantially after stabilization of external environmental drivers.

scholarly journals Climate change will cause non-analogue vegetation states in Africa and commit vegetation to long-term change

2020 ◽  
Author(s):  
Mirjam Pfeiffer ◽  
Dushyant Kumar ◽  
Carola Martens ◽  
Simon Scheiter
Keyword(s):  
Euclidean Distance ◽  
Vegetation Change ◽  
Equilibrium States ◽  
Tree Cover ◽  
Environmental Drivers ◽  
State Variables ◽  
Rcp Scenarios ◽  
Lag Times ◽  
Over Time

Abstract. Vegetation responses to changes in environmental drivers can be subject to temporal lags. This implies that vegetation is committed to future changes once environmental drivers stabilize. Understanding the trajectories of such committed changes is important as they affect future carbon storage, vegetation structure and community composition and therefore need consideration in conservation management. In this study, we investigate whether transient vegetation states can be represented by a time-shifted trajectory of equilibrium vegetation states, or if they are vegetation states without analogue in conceivable equilibrium states. We use a dynamic vegetation model, the aDGVM, to assess deviations between simulated transient and equilibrium vegetation states in Africa between 1970 and 2099 for the RCP4.5 and 8.5 scenarios. Euclidean distance between simulated transient and equilibrium vegetation states based on selected state variables was used to determine lag times and similarity of vegetation states. We found that transient vegetation states over time increasingly deviated from equilibrium states in both RCP scenarios, but that deviation was more pronounced in RCP8.5 during the second half of the 21st century. Trajectories of transient vegetation change did not follow a virtual trajectory of equilibrium states, but represented non-analogue composite states resulting from multiple lags with respect to vegetation processes and composition. Lag times between transient and most similar equilibrium vegetation states increased over time and were most pronounced in savanna and woodland areas, where disequilibrium in savanna tree cover frequently acted as main driver for dissimilarities. Fire additionally enhanced lag times and Euclidean distance between transient and equilibrium vegetation states due to its restraining effect on vegetation succession. Long lag times can be indicative of high rates of change in environmental drivers, of meta-stability and non-analogue vegetation states, and of augmented risk for future tipping points. For long-term planning, conservation managers should therefore strongly focus on areas where such long lag times and high residual Euclidean distance between most similar transient and equilibrium vegetation states have been simulated.

scholarly journals African biomes are most sensitive to changes in CO<sub>2</sub> under recent and near-future CO<sub>2</sub> conditions

2020 ◽  
Vol 17 (4) ◽  
pp. 1147-1167 ◽  
Author(s):  
Simon Scheiter ◽  
Glenn R. Moncrieff ◽  
Mirjam Pfeiffer ◽  
Steven I. Higgins
Keyword(s):  
Environmental Conditions ◽  
Climate Model ◽  
Mitigation Strategies ◽  
Tree Cover ◽  
Mixing Ratio ◽  
Vegetation Model ◽  
Rcp Scenarios ◽  
Dynamic Global Vegetation Model ◽  
Lag Effects ◽  
Near Future

Abstract. Current rates of climate and atmospheric change are likely higher than during the last millions of years. Even higher rates of change are projected in CMIP5 climate model ensemble runs for some Representative Concentration Pathway (RCP) scenarios. The speed of ecological processes such as leaf physiology, demography or migration can differ from the speed of changes in environmental conditions. Such mismatches imply lags between the actual vegetation state and the vegetation state expected under prevailing environmental conditions. Here, we used a dynamic vegetation model, the adaptive Dynamic Global Vegetation Model (aDGVM), to study lags between actual and expected vegetation in Africa under a changing atmospheric CO2 mixing ratio. We hypothesized that lag size increases with a more rapidly changing CO2 mixing ratio as opposed to slower changes in CO2 and that disturbance by fire further increases lag size. Our model results confirm these hypotheses, revealing lags between vegetation state and environmental conditions and enhanced lags in fire-driven systems. Biome states, carbon stored in vegetation and tree cover in Africa are most sensitive to changes in CO2 under recent and near-future levels. When averaged across all biomes and simulations with and without fire, times to reach an equilibrium vegetation state increase from approximately 242 years for 200 ppm to 898 years for 1000 ppm. These results have important implications for vegetation modellers and for policy making. Lag effects imply that vegetation will undergo substantial changes in distribution patterns, structure and carbon sequestration even if emissions of fossils fuels and other greenhouse gasses are reduced and the climate system stabilizes. We conclude that modelers need to account for lag effects in models and in data used for model testing. Policy makers need to consider lagged responses and committed changes in the biosphere when developing adaptation and mitigation strategies.

scholarly journals Landscape Change and Trade in Ancient Greece: Evidence from Pollen Data

2020 ◽  
Vol 130 (632) ◽  
pp. 2596-2618
Author(s):  
Adam Izdebski ◽  
Tymon Słoczyński ◽  
Anton Bonnier ◽  
Grzegorz Koloch ◽  
Katerina Kouli
Keyword(s):  
Environmental History ◽  
Agricultural Production ◽  
Landscape Change ◽  
Vegetation Change ◽  
Structural Changes ◽  
Ancient Greece ◽  
Pollen Data ◽  
Trade Expansion ◽  
Southern Greece

Abstract In this article we use pollen data from six sites in southern Greece to study long-term vegetation change in this region from 1000 BCE to 600 CE. Based on insights from environmental history, we interpret our estimated trends in the regional presence of cereal, olive and vine pollen as proxies for structural changes in agricultural production. We present evidence that there was a market economy in ancient Greece and a major trade expansion several centuries before the Roman conquest. Our results are consistent with auxiliary data on settlement dynamics, shipwrecks and ancient oil and wine presses.

Vegetation change in an urban grassy woodland 1974 - 2000

2004 ◽  
Vol 52 (5) ◽  
pp. 597 ◽  
Author(s):  
J. B. Kirkpatrick
Keyword(s):  
Species Richness ◽  
Species Composition ◽  
Exotic Species ◽  
Native Species ◽  
Vegetation Change ◽  
Structural Changes ◽  
Linear Models ◽  
Tree Cover ◽  
Native Plant ◽  
Native Species Richness

Few temporal studies document vegetation change in Australian temperate grassy woodlands. Floristic and structural data were collected from 68 randomly located sites in the Queens Domain, an urban grassy woodland remnant, in 1974, 1984, 1994 and 2000 and a search made for rare species. Species of conservation significance were concentrated at highly disturbed sites, whereas vegetation types of conservation significance decreased in area as a result of increases in the numbers of Allocasuarina verticillata, which caused a change in many unmown areas from Eucalyptus viminalis grassy woodland to E. viminalis–A. verticillata woodland/forest or A. verticillata open/closed forest. Structural changes were associated with changes in species composition and an increase in native-species richness. Increases in tree cover occurred where fires were most frequent, possibly as a result of the lack of mammalian herbivores. The frequencies of herbs and annual grasses were strongly affected by precipitation in the month of sampling. Half of the species that showed a consistent rise or fall through time were woody plants, approximately twice the number expected. In the dataset as a whole, species-richness variables were largely explained by varying combinations of variables related to moisture availability, altitude and the incidence of mowing. The strongest influences on species composition were the same, although slope and time since the last fire also contributed to multiple regression and generalised linear models. Compositional stability was positively related to native-species richness, whereas high levels of exotic-species richness occurred at both low and high levels of native-species richness. The maintenance of native-plant biodiversity on the Domain requires such counterintuitive measures as the maintenance of exotic trees and the control of native trees, demonstrating the contingencies of conservation management in fragmented vegetation that consists of a mixture of native and exotic species.

scholarly journals Spaceborne potential for examining taiga–tundra ecotone form and vulnerability

2016 ◽  
Vol 13 (13) ◽  
pp. 3847-3861 ◽  
Author(s):  
Paul M. Montesano ◽  
Guoqing Sun ◽  
Ralph O. Dubayah ◽  
K. Jon Ranson
Keyword(s):  
Forest Structure ◽  
Vegetation Change ◽  
Structural Changes ◽  
Vertical Component ◽  
Tree Cover ◽  
Maximum Height ◽  
Forest Patches ◽  
Forest Patch ◽  
Forest Height ◽  
Patch Scale

Abstract. In the taiga–tundra ecotone (TTE), site-dependent forest structure characteristics can influence the subtle and heterogeneous structural changes that occur across the broad circumpolar extent. Such changes may be related to ecotone form, described by the horizontal and vertical patterns of forest structure (e.g., tree cover, density, and height) within TTE forest patches, driven by local site conditions, and linked to ecotone dynamics. The unique circumstance of subtle, variable, and widespread vegetation change warrants the application of spaceborne data including high-resolution (< 5 m) spaceborne imagery (HRSI) across broad scales for examining TTE form and predicting dynamics. This study analyzes forest structure at the patch scale in the TTE to provide a means to examine both vertical and horizontal components of ecotone form. We demonstrate the potential of spaceborne data for integrating forest height and density to assess TTE form at the scale of forest patches across the circumpolar biome by (1) mapping forest patches in study sites along the TTE in northern Siberia with a multi-resolution suite of spaceborne data and (2) examining the uncertainty of forest patch height from this suite of data across sites of primarily diffuse TTE forms. Results demonstrate the opportunities for improving patch-scale spaceborne estimates of forest height, the vertical component of TTE form, with HRSI. The distribution of relative maximum height uncertainty based on prediction intervals is centered at  ∼  40 %, constraining the use of height for discerning differences in forest patches. We discuss this uncertainty in light of a conceptual model of general ecotone forms and highlight how the uncertainty of spaceborne estimates of height can contribute to the uncertainty in identifying TTE forms. A focus on reducing the uncertainty of height estimates in forest patches may improve depiction of TTE form, which may help explain variable forest responses in the TTE to climate change and the vulnerability of portions of the TTE to forest structure change.

scholarly journals A novel suprachoroidal microinvasive glaucoma implant: in vivo biocompatibility and biointegration

2020 ◽  
Vol 2 (1) ◽  
Author(s):  
Ian Grierson ◽  
Don Minckler ◽  
Marian K. Rippy ◽  
Andrew J. Marshall ◽  
Nathalie Collignon ◽  
...  
Keyword(s):  
Intraocular Pressure ◽  
Time Course ◽  
Structural Changes ◽  
Ocular Tissues ◽  
Tissue Integration ◽  
Drainage Channels ◽  
Pressure Lowering ◽  
Over Time

Abstract Background A major challenge for any glaucoma implant is their ability to provide long-term intraocular pressure lowering efficacy. The formation of a low-permeability fibrous capsule around the device often leads to obstructed drainage channels, which may impair the drainage function of devices. These foreign body-related limitations point to the need to develop biologically inert biomaterials to improve performance in reaching long-term intraocular pressure reduction. The aim of this study was to evaluate in vivo (in rabbits) the ocular biocompatibility and tissue integration of a novel suprachoroidal microinvasive glaucoma implant, MINIject™ (iSTAR Medical, Wavre, Belgium). Results In two rabbit studies, no biocompatibility issue was induced by the suprachoroidal, ab-externo implantation of the MINIject™ device. Clinical evaluation throughout the 6 post-operative months between the sham and test groups were similar, suggesting most reactions were related to the ab-externo surgical technique used for rabbits, rather than the implant material itself. Histological analysis of ocular tissues at post-operative months 1, 3 and 6 revealed that the implant was well-tolerated and induced only minimal fibroplasia and thus minimal encapsulation around the implant. The microporous structure of the device became rapidly colonized by cells, mostly by macrophages through cell migration, which do not, by their nature, impede the flow of aqueous humor through the device. Time-course analysis showed that once established, pore colonization was stable over time. No fibrosis nor dense connective tissue development were observed within any implant at any time point. The presence of pore colonization may be the process by which encapsulation around the implant is minimized, thus preserving the permeability of the surrounding tissues. No degradation nor structural changes of the implant occurred during the course of both studies. Conclusions The novel MINIject™ microinvasive glaucoma implant was well-tolerated in ocular tissues of rabbits, with observance of biointegration, and no biocompatibility issues. Minimal fibrous encapsulation and stable cellular pore colonization provided evidence of preserved drainage properties over time, suggesting that the implant may produce a long-term ability to enhance aqueous outflow.

scholarly journals Dynamics of Individual Income Rank Volatility: Evidence from West Germany and the US

2019 ◽  
Vol 19 (2) ◽  
Author(s):  
Louis Chauvel ◽  
Anne Hartung ◽  
Flaviana Palmisano
Keyword(s):  
Structural Changes ◽  
West Germany ◽  
Marginal Distributions ◽  
Individual Income ◽  
The Us ◽  
Long Term Trends ◽  
Over Time

Abstract This paper presents a methodology for comparing income rank volatility profiles over time and across distributions. While most of the existing measures are affected by changes in marginal distributions, this paper proposes a framework based on individuals’ relative positions in the distribution that is neutral to structural changes that occur in that distribution. Applying this approach to West Germany and the US over three decades, we show that while poorer individuals in both countries are the most volatile in all periods investigated, the long-term trends of volatility at the different points of the distribution in each of these countries differ.

Provenance description of metadata application profiles for long-term maintenance of metadata schemas

2018 ◽  
Vol 74 (1) ◽  
pp. 36-61 ◽  
Author(s):  
Chunqiu Li ◽  
Shigeo Sugimoto
Keyword(s):  
Structural Changes ◽  
Public Library ◽  
Structural Features ◽  
Dublin Core ◽  
Content Type ◽  
Metadata Schema ◽  
Proposed Model ◽  
Application Profile ◽  
Over Time

Purpose Provenance information is crucial for consistent maintenance of metadata schemas over time. The purpose of this paper is to propose a provenance model named DSP-PROV to keep track of structural changes of metadata schemas. Design/methodology/approach The DSP-PROV model is developed through applying the general provenance description standard PROV of the World Wide Web Consortium to the Dublin Core Application Profile. Metadata Application Profile of Digital Public Library of America is selected as a case study to apply the DSP-PROV model. Finally, this paper evaluates the proposed model by comparison between formal provenance description in DSP-PROV and semi-formal change log description in English. Findings Formal provenance description in the DSP-PROV model has advantages over semi-formal provenance description in English to keep metadata schemas consistent over time. Research limitations/implications The DSP-PROV model is applicable to keep track of the structural changes of metadata schema over time. Provenance description of other features of metadata schema such as vocabulary and encoding syntax are not covered. Originality/value This study proposes a simple model for provenance description of structural features of metadata schemas based on a few standards widely accepted on the Web and shows the advantage of the proposed model to conventional semi-formal provenance description.

scholarly journals Exploring Surface Biophysical-Climate Sensitivity to Tropical Deforestation Rates Using a GCM: A Feasibility Study*

2012 ◽  
Vol 16 (4) ◽  
pp. 1-23 ◽  
Author(s):  
C. Kendra Gotangco Castillo ◽  
Kevin Robert Gurney
Keyword(s):  
Climate Sensitivity ◽  
Amazon Basin ◽  
Forest Cover ◽  
Tropical Deforestation ◽  
Tree Cover ◽  
Dynamic Global Vegetation Model ◽  
Climate System Model ◽  
Deforestation Rates ◽  
Global Vegetation

Abstract Deforestation perturbs both biophysical and carbon feedbacks on climate. However, biophysical feedbacks operate at temporally immediate and spatially focused scales and thus may be sensitive to the rate of deforestation rather than just to total forest-cover loss. Explored here is a method for simulating annual tropical deforestation in the fully coupled Community Climate System Model, version 3.0 (CCSM3) with the Dynamic Global Vegetation Model (DGVM) for testing biosphere climate sensitivity to “preservation pathways.” Two deforestation curves were simulated—a 10% deforestation curve with a 10% preservation target (DFC10-PT10) versus a 1% deforestation curve with a 10% preservation target (DFC1-PT10). During active deforestation, albedo, net radiation, latent heat flux, and climate variables were compared for time dependence and sensitivity to tropical tree cover across the tropical band and the Amazon basin, central African, and Southeast Asian regions. The results demonstrated the feasibility of modeling incremental deforestation and detecting both transient and long-term impacts, although a warm/dry bias in CCSM3–DGVM and the absence of carbon feedbacks preclude definitive conclusions on the magnitude of sensitivities. The deforestation rates produced characteristic trends in biophysical variables with DFC10-PT10 resulting in rapid increase/decrease during the initial 10–30 years before leveling off, whereas DFC1-PT10 exhibits gradual changes. The rate had little effect on biophysical and climate sensitivities when averaged over tropical land but produced significant differences at a regional level. Over the long term, the rates produced dissimilar vegetation distributions, despite having the same preservation target in both cases. Overall, these results indicate that the question of rates is one worth further analysis.

Grazing exclosures reveal divergent patterns of change in bunchgrass grasslands of Western Canada

Botany ◽  
2021 ◽  
Vol 99 (1) ◽  
pp. 9-22
Author(s):  
Gary E. Bradfield ◽  
W.F. Preston Cumming ◽  
Reg F. Newman ◽  
Maja Krzic
Keyword(s):  
Vegetation Change ◽  
Structural Changes ◽  
Poa Pratensis ◽  
Kentucky Bluegrass ◽  
Growing Seasons ◽  
South Central ◽  
Species Cover ◽  
Rough Fescue ◽  
Dominant Grasses

Thirty-six long-term (14–83 years) cattle grazing exclosures and adjacent grazed pastures spanning a climatic gradient from cooler–wetter to warmer–drier growing seasons in south-central British Columbia were compared for temporal vegetation change. Trajectories of temporal vegetation change from non-metric multidimensional scaling were mostly scattered for the grazed areas, but more directed toward the dominant grasses, primarily rough fescue (Festuca campestris) or Kentucky bluegrass (Poa pratensis), for the exclosures. Plant community differences, detected only after 10 years of grazing exclusion, were primarily due to structural shifts in overall species cover related to growth increases of the dominant grasses inside exclosures. Species richness remained unchanged between the first and last sampling dates in both grazed areas and exclosures, with both treatments showing moderate degrees (15%–30%) of turnover in species composition. Shannon diversity declined in both treatments as a result of the structural changes in species cover. The results highlight the value of repeated monitoring of long-term exclosures for assessment of grassland resiliency to grazing. Further studies of the interaction of grazing and climate are needed for a more complete understanding of the ongoing vegetation change.

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